[BOLT] Gadget scanner: detect non-protected indirect calls

Author: atrosinenko

bolt/include/bolt/Core/MCPlusBuilder.h

@@ -577,6 +577,16 @@ class MCPlusBuilder {
     return getNoRegister();
   }
 
+  /// Returns the register used as call destination, or no-register, if not
+  /// an indirect call. Sets IsAuthenticatedInternally if the instruction
+  /// accepts signed pointer as its operand and authenticates it internally.
+  virtual MCPhysReg
+  getRegUsedAsCallDest(const MCInst &Inst,
+                       bool &IsAuthenticatedInternally) const {
+    llvm_unreachable("not implemented");
+    return getNoRegister();
+  }
+
   virtual bool isTerminator(const MCInst &Inst) const;
 
   virtual bool isNoop(const MCInst &Inst) const {

bolt/lib/Passes/PAuthGadgetScanner.cpp

@@ -382,11 +382,11 @@ class PacRetAnalysis
 
 public:
   std::vector<MCInstReference>
-  getLastClobberingInsts(const MCInst Ret, BinaryFunction &BF,
-                         const ArrayRef<MCPhysReg> UsedDirtyRegs) const {
+  getLastClobberingInsts(const MCInst &Inst, BinaryFunction &BF,
+                         const ArrayRef<MCPhysReg> UsedDirtyRegs) {
     if (RegsToTrackInstsFor.empty())
       return {};
-    auto MaybeState = getStateAt(Ret);
+    auto MaybeState = getStateBefore(Inst);
     if (!MaybeState)
       llvm_unreachable("Expected State to be present");
     const State &S = *MaybeState;
@@ -434,6 +434,29 @@ shouldReportReturnGadget(const BinaryContext &BC, const MCInstReference &Inst,
   return std::make_shared<GadgetReport>(RetKind, Inst, RetReg);
 }
 
+static std::shared_ptr<Report>
+shouldReportCallGadget(const BinaryContext &BC, const MCInstReference &Inst,
+                       const State &S) {
+  static const GadgetKind CallKind("non-protected call found");
+  if (!BC.MIB->isCall(Inst) && !BC.MIB->isBranch(Inst))
+    return nullptr;
+
+  bool IsAuthenticated = false;
+  MCPhysReg DestReg = BC.MIB->getRegUsedAsCallDest(Inst, IsAuthenticated);
+  if (IsAuthenticated || DestReg == BC.MIB->getNoRegister())
+    return nullptr;
+
+  LLVM_DEBUG({
+    traceInst(BC, "Found call inst", Inst);
+    traceReg(BC, "Call destination reg", DestReg);
+    traceRegMask(BC, "SafeToDerefRegs", S.SafeToDerefRegs);
+  });
+  if (S.SafeToDerefRegs[DestReg])
+    return nullptr;
+
+  return std::make_shared<GadgetReport>(CallKind, Inst, DestReg);
+}
+
 FunctionAnalysisResult
 Analysis::findGadgets(BinaryFunction &BF,
                       MCPlusBuilder::AllocatorIdTy AllocatorId) {
@@ -450,10 +473,12 @@ Analysis::findGadgets(BinaryFunction &BF,
   for (BinaryBasicBlock &BB : BF) {
     for (int64_t I = 0, E = BB.size(); I < E; ++I) {
       MCInstReference Inst(&BB, I);
-      const State &S = *PRA.getStateAt(Inst);
+      const State &S = *PRA.getStateBefore(Inst);
 
       if (auto Report = shouldReportReturnGadget(BC, Inst, S))
         Result.Diagnostics.push_back(Report);
+      if (auto Report = shouldReportCallGadget(BC, Inst, S))
+        Result.Diagnostics.push_back(Report);
     }
   }
   return Result;

bolt/lib/Target/AArch64/AArch64MCPlusBuilder.cpp

@@ -277,6 +277,48 @@ class AArch64MCPlusBuilder : public MCPlusBuilder {
     }
   }
 
+  MCPhysReg
+  getRegUsedAsCallDest(const MCInst &Inst,
+                       bool &IsAuthenticatedInternally) const override {
+    assert(isCall(Inst) || isBranch(Inst));
+    IsAuthenticatedInternally = false;
+
+    switch (Inst.getOpcode()) {
+    case AArch64::B:
+    case AArch64::BL:
+      assert(Inst.getOperand(0).isExpr());
+      return getNoRegister();
+    case AArch64::Bcc:
+    case AArch64::CBNZW:
+    case AArch64::CBNZX:
+    case AArch64::CBZW:
+    case AArch64::CBZX:
+      assert(Inst.getOperand(1).isExpr());
+      return getNoRegister();
+    case AArch64::TBNZW:
+    case AArch64::TBNZX:
+    case AArch64::TBZW:
+    case AArch64::TBZX:
+      assert(Inst.getOperand(2).isExpr());
+      return getNoRegister();
+    case AArch64::BR:
+    case AArch64::BLR:
+      return Inst.getOperand(0).getReg();
+    case AArch64::BRAA:
+    case AArch64::BRAB:
+    case AArch64::BRAAZ:
+    case AArch64::BRABZ:
+    case AArch64::BLRAA:
+    case AArch64::BLRAB:
+    case AArch64::BLRAAZ:
+    case AArch64::BLRABZ:
+      IsAuthenticatedInternally = true;
+      return Inst.getOperand(0).getReg();
+    default:
+      llvm_unreachable("Unhandled call instruction");
+    }
+  }
+
   bool isADRP(const MCInst &Inst) const override {
     return Inst.getOpcode() == AArch64::ADRP;
   }